Crosspoint switches are commercially available products that selectively route a plurality of input signals to a plurality of output terminals (for example, J inputs to K outputs), where each output is connected to at most a single input signal. Their usefulness arises from the need to connect source signals (video and audio, for example) to multiple loads (video monitors, for example), where the connectivity matrix can be conveniently reprogrammed via a digital interface.
Crosspoint switches may be manufactured as integrated circuits. Crosspoint die size has increased steadily with products that provide increasingly larger input and output counts. For example, at the time of this writing, 32×32 or 48×27 crosspoints are commercially available. Larger die sizes have led to larger parasitics capacitances within circuit components which can limit a switch's dynamic performance. Two such limiting factors are the sheer length of each signal line within each slice—the length of the wires themselves—and the number of circuit elements connected to them. Parasitic capacitance, unless remedied, limits the size and performance of crosspoint switches.
FIG. 7 is a circuit diagram that illustrates the effects of parasitic capacitance in an amplifier circuit that includes an operational amplifier 710 in a non-inverting configuration. There, the circuit 700 may include an input signal coupled to a positive input terminal and a feedback circuit coupling to the output terminal, the negative input terminal and ground. Consider first a circumstance where the feedback circuit includes resistors RF and RG. When the operational amplifier 710 is manufactured as an integrated circuit, parasitic capacitances commonly are created between the negative input terminal and ground due to effects created by circuit packaging and layout. FIG. 7 models this parasitic capacitance as CPAR. Excess parasitic capacitance can cause problems with ringing in response to a time-varying input signal, poor settling times and, in extreme cases, oscillatory behavior. FIG. 7 also illustrates a feedback capacitor provided between the output terminal and the negative input terminal which combats the effects of parasitic capacitance. The feedback capacitor combats phase delays that might be introduced by the parasitic capacitance and, therefore, remedies performance problems associated with the ringing, settling times and oscillation. As noted, however, the feedback capacitor is a discrete element, which is provided as an external component. A multi-output crosspoint switch will have many such amplifiers and, therefore, would need many feedback capacitors.
There is a need in the art for a crosspoint switch design that minimizes parasitic capacitance of circuit components. Further, there is a need for a crosspoint switch design that reduces or eliminates the need for external feedback capacitors in their design.